Cast iron material, seal material and the production method

ABSTRACT

A cast iron material composed of C, Si, Mn, Ni, Cr and the rest composed of Fe and inevitable impurities, wherein contents of said C, Si, Mn, Ni and Cr with respect to the entire cast iron material are C: 2.9 to 3.8 wt %, Si: 1.0 to 2.5 wt %, Mn: 0 to 0.8 wt % (note that 0 is not included), Ni: 3.5 to 5.0 wt %, and Cr: 2.6 to 5.5 wt %. According to the present invention, a cast iron material having high hardness and excellent wear resistance and a seal material for a floating seal, formed by the cast iron material can be provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cast iron material, a seal material for a floating seal, and the production method, and particularly relates to a cast iron material and a seal ring material for a floating seal of construction machines and vehicles, having high hardness, excellent wear-and-abrasive resistance, and the production method.

2. Description of the Related Art

A floating seal apparatus is used as a seal for track rollers of construction machines and vehicles, to prevent dirt from intruding into the rollers and to prevent inner lubricating oil from leaking to the outside. A floating seal apparatus comprises a pair of floating seal rings on a stationary side and a rotatable side and is installed around a shaft in a state of not contacting the shaft, that is, in a state of floating from the shaft. Also, the floating seal rings on the stationary side and rotatable side respectively have a sliding surface facing to each other for mutually contacting by sliding and are used in a state of facing to each other via the sliding surfaces.

The respective floating seal rings on the stationary side and the rotatable side are incorporated respectively in a mechanism on the stationary side and a mechanism on the rotatable side via O-rings, and both of the floating seal rings are pressured to contact by an elastic force of the O-rings via the sliding surfaces. Accordingly, it is possible to seal between the mechanism on the stationary side and the mechanism on the rotatable side regardless of whether it is rotating or not rotating and to prevent intrusion of muddy water, earth and sand, etc. to inside the roller and leakage of lubricating oil to the outside.

A material composing a floating seal ring as above is requited to have high hardness, excellent wear-and-abrasive resistance, etc., and cast iron, etc. produced by a casting method has been conventionally used. As cast iron as such, for example, high-chromium cast iron, chrome-molybdenum cast iron and nickel-chrome cast iron, etc. are used (for example, the Japanese Unexamined Patent Publications No. 6-109141 and No. 6-114538).

High-chrome cast iron and chrome-molybdenum cast iron are materials having high hardness. Particularly, chrome-molybdenum cast iron having approximately the same structure with that of high-chrome cast iron and having a Mo content of 2 to 4 wt % has high hardness as 64 or so in HRC. However, high-chrome cast iron and chrome-molybdenum cast iron are subjected to thermal treatment of hardening, etc. for obtaining high hardness, and a large internal load is imposed on the material itself by the thermal treatment, so that it is liable that the physical strength becomes very brittle.

As nickel-chrome cast iron, for example, Ni-hard cast iron, etc. may be mentioned. Ni-hard cast iron has a Ni content of 3.5 to 5.0 wt % or so and has martensitic matrix, and the wear resistance is excellent. However, similar to the above high-chrome cast iron, Ni-hard cast iron is also subjected to thermal treatment of low temperature annealing, etc. for improving the toughness and wear resistance, so that although high-toughness is attained, the physical strength is liable to become very brittle.

Also, the Japanese Unexamined Patent Publication No. 2002-098236 discloses a floating seal ring using a sintered alloy produced by a powder metallurgical method as a constituent material. Such a floating seal ring produced by a sintered alloy has a high degree of freedom in a material composition comparing with a floating seal ring made by cast iron produced by the above casting method, therefore, there is an advantage of being excellent in dimensional precision. Also, a physical property of a sintered alloy produced by a powder metallurgical method depends on the material composition, so that it is necessary to adjust the material composition to change a physical property of the sintered alloy. However, an improvement of a physical property is limited only by adjusting the material composition, and wear resistance and other properties are insufficient when using a sintered alloy as a material for forming a floating seal ring.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a cast iron material having high hardness, excellent wear-and-abrasive resistance, a floating seal and other seal materials formed by the cast iron material, and the production method.

The present inventors found that the above object can be attained by making a content of elements other than Cr in a cast iron material used for a seal material for a floating seal, approximately as same as that in the above Ni-hard cast iron and setting a Cr content to 2.6 to 5.5 wt % with respect to the entire cast iron, and completed the present invention.

Namely, according to the present invention, there is provided a cast iron material composed of C, Si, Mn, Ni, Cr and the rest composed of Fe and inevitable impurities, wherein

-   -   contents of the C, Si, Mn, Ni and Cr with respect to the entire         cast iron material are     -   C: 2.9 to 3.8 wt %,     -   Si: 1.0 to 2.5 wt %,     -   Mn: 0 to 0.6 wt % (note that 0 is not included),     -   Ni: 3.5 to 5.0 wt %, and     -   Cr: 2.6 to 5.5 wt %.

In the cast iron material according to the present invention, preferably, contents of P and S in the inevitable impurities with respect to the entire cast iron material are P: 0.5 wt % or lest and 8: 0.5 wt % or less.

P is compounded with iron to form steadite (Fe₃P), which results in a tendency of declining a cutting property of cast iron and making cast iron brittle. S makes a coagulation point of the cast iron high, which results in a tendency of deteriorating a flow property of molten metal and making cast iron after casting brittle. Therefore, the smaller a content of P and S is in inevitable impurities in cast iron, the better.

In the cast iron material according to the present invention, preferably, a matrix structure is a structure selected from perlite, bainite and martensite, or a mixed structure of these, and has a fine structure consisting of dendritic cementite and carbides of Cr.

In the present invention, the matrix structure is more preferably a mixed structure, wherein martensite is the main body, and furthermore preferably a mixed structure of perlite and martensite, wherein martensite is the main body.

In the cast iron material according to the present invention, preferably, hardness of the cast iron material is 62 or higher, more preferably 65 or higher in HRC.

A seal material of the present invention is formed by any one of the above explained cast iron materials. The seal material is not particularly limited and, for example, a mechanical seal and floating seal, etc. may be mentioned and, particularly, a floating seal for track rollers is preferable.

Since a floating seal ring of the present invention is formed by the above seal material and has high hardness, excellent wear resistance and corrosion resistance, it is preferable to be used as a seal for track rollers of construction machines and vehicles.

According to the present invention, there is provided a production method of a seal material, including steps of casting in a mold a molten metal composed of C, Si, Mn, Ni, Cr and the rest composed of Fe and inevitable impurities, and curing by cooling, wherein

-   -   contents of the C, Si, Mn, Ni and Cr with respect to the entire         molten metal are     -   C: 2.9 to 3.8 wt %,     -   Si: 1.0 to 2.5 wt %,     -   Mn: 0 to 0.9 wt % (note that 0 is not included),     -   Ni: 3.5 to 5.0 wt %, and     -   Cr: 2.6 to 5.5 wt %;     -   wherein a cooling rate at a position of a sliding surface of the         seal material is higher than that on other parts when curing by         cooling.

In a production method of the seal material of the present invention, molten metal is made to be in a composition range of the present invention and a sliding surface position to be a seal surface is forcibly and preferentially cooled at a higher cooling rate comparing with that on other parts, so that it is possible to form a fine structure on the sliding surface and, particularly, it is possible to improve hardness and wear resistance of the sliding surface. Also, as a fine structure, a structure, wherein dendritic cementite and fine carbides mainly including Cr are dispersed and the matrix structure is selected from perlite, bainite and martensite or a mixed structure of these, is preferable.

In the production method of the seal material according to the present invention, preferably, contents of P and S in the inevitable impurities with respect to the entire cast iron material are P: 0.5 wt % or less and SC 0.5 wt % or less.

In the production method of the seal material according to the present invention, when the cooling rate (° C./min.) at the sliding surface position of the above seal material is C_(R)1 and the cooling rate (° C./min.) on other parts is C_(R)2, preferably, 1≦C_(R)1/C_(R)≦2.5.

Alternately, in the production method of the seal material according to the present invention, preferably, the cooling rate at the time of cooling and curing the sliding surface position is preferably 300 to 700° C./min., and more preferably 500 to 700° C./min.

According to the present invention, as a result that a component composition composing a cast iron material is made to be in the above predetermined range, that is, a content of elements other than Cr is approximately as same as that in Ni-hard cast iron and a Cr content is made to be 2.6 to 5.5 wt % with respect to the entire cast iron, it is possible to provide a cast iron material having high hardness, excellent wear-and-abrasive resistance. Also, by using the cast iron material of the present invention as a material composing a seal material, it is possible to provide a floating seal and other seal materials having the above properties.

Furthermore, according to a production method of a seal material of the present invention, molten metal is made to be in a composition range of the present invention, and a sliding surface position to be a seal surface of a seal material is forcibly and preferentially cooled at a higher cooling rate comparing with that on other parts, so that it is possible to form a fine structure on the sliding surface, and particularly, it is possible to provide a floating seal and other seal materials having high hardness, excellent wear-and-abrasive resistance,

BRIEF DESCRIPTION OF THE DRAWINGS

Below, embodiments of the present invention will be explained in detail based on drawings, in which:

FIG. 1 is a sectional view of a floating seal apparatus according to an embodiment of the present invention;

FIG. 2A and FIG. 2B are views of surface roughness of a worn state after a wear resistance test on a sliding surface of samples of an example and a comparative example of the present invention; and

FIG. 3A and FIG. 3B are views of a moving amount on the inside circumferential side of a seal band after a wear resistance test on samples of an example and a comparative example of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Floating Seal Apparatus 1

As shown in FIG. 1, a floating seal apparatus 1 according to an embodiment of the present invention comprises a floating seal ring 2 on the stationary side and a floating seal ring 7 on the rotatable side, made to be a pair. The floating seal rings are installed around a shaft 20 in a state of not contacting the shaft 20, that is, in a state of floating from the shaft 20.

The floating seal ring 2 on the stationary side is combined with a stationary housing 12 via an O-ring 18, and the floating seal ring 7 on the rotatable side is combined with a rotatable housing 15 via an O-ring 19.

The floating seal ring 2 on the stationary side has a ring structure having a larger inner diameter than an outer diameter of the shaft 20, and a groove 3 of a predetermined depth is provided on the outer circumferential surface. On a bottom surface of the groove 3 is formed a taper surface 4 gradually getting closer to the shaft 20 as it gets farther from the floating seal ring 7 on the rotatable side.

Similarly, the floating seal ring 7 on the rotatable side has a ring structure having a larger inner diameter than an outer diameter of the shaft 20, and a groove 8 of a predetermined depth is provided on the outer circumferential surface, The groove 8 is formed with a taper surface 9.

The floating seal ring 2 on the stationary side and the floating seal ring 7 on the rotatable side respectively have a sliding surface 5 and a sliding surface 10 on its outer circumference part on the facing surfaces, and both of the floating seal rings face to each other via the sliding surface 5 and the sliding surface 10.

Also, on a surface of the floating seal ring 2 on the stationary side facing to the floating seal ring 7 on the rotatable side, a part on an inner circumferential side continuing to the sliding surface 5 is formed with a taper surface 6 gradually getting farther from the floating seal ring 7 on the rotatable side as it gets closer to the shaft 20.

Similarly, on a surface of the floating seal ring 7 on the rotatable side facing to the floating seal ring 2 on the stationary side, a part on an inner circumferential side continuing to the sliding surface 10 is formed with a taper surface 11.

The stationary housing 12 is fixed to one end portion of the shaft 20 and surrounds by its inner circumferential surface an outer circumferential surface of the floating seal ring 2 on the stationary side. The inner circumferential surface of the stationary housing 12 is provided with a groove 13 having a predetermined depth, and the groove 13 is formed with a taper surface 14 slanting to the same direction as that of the bottom surface of the groove 3 on the outer circumferential surface of the floating seal ring 2 on the stationary side.

The rotatable housing 15 is provided to be able to freely rotate on the other end portion of the shaft 20 via a shaft bearing (not shown) and surrounds by its inner circumferential surface the outer circumferential surface of the floating seal ring 7 on the rotatable side. On the inner circumferential surface of the rotatable housing 15 is provided with a groove 16 having a predetermined depth over the entire circumference, and the groove 16 is formed with a taper surface 17 slanting to the same direction of that of the bottom surface of the groove 8 on the outer circumferential surface of the floating seal ring 7 on the rotatable side.

Also, the floating seal ring 2 on the stationary side and the stationary housing 12, and the floating seal ring 7 on the rotatable side and the rotatable housing 15 are combined respectively via the O-ring 18 and the O-ring 19, and the O-rings 18 and 19 are formed by an elastic material. It is configured that, due to an elastic force of the O-rings 18 and 19, the floating seal ring 2 on the stationary side and the floating seal ring 7 on the rotatable side are pressured to contact via the sliding surface 5 and the sliding surface 10, and between the sliding surfaces 5 and 10 is sealed regardless of whether the rotatable housing 15 is rotating or not rotating.

Stationary Side and Rotatable Side Floating Seal Rings 2 and 7

The floating seal ring 2 on the stationary side and the floating seal ring 7 on the rotatable side are formed by a cast iron material of the present invention.

The cast iron material of the present invention is composed of C (carbon), Si (silicon), Mn (manganese), Ni (nickel), Cr (chrome) and the rest composed of Fe (iron) and inevitable impurities.

C (carbon) is capable of controlling an amount of carbide, such as cementite forming the chill structure, by changing the content. Also, C has an effect of accelerating dendritic crystallization of crystal grains and adjusting a base material structure. A content of C is 2.5 to 4.0 wt %, preferably 2.9 to 3.8 wt %, and more preferably 3.2 to 3.7 wt % with respect to the entire cast iron material. When the C content is too small, a content of cementite in the fine structure becomes small and wear resistance and machinability of the base material tend to decline, When the content is too large, cementite in the chill structure becomes coarse and cavities due to remelting are easily caused in the fine structure, furthermore, an amount of graphite increases and strength of cast iron tends to decline.

Si (silicon) has an effect of extricating carbon from pig iron and accelerating graphitization of cast iron after casting, while, has an effect of causing dendritic crystallization or columnar crystallization of crystal grains. A content of Si is 1.0 to 3.0 wt %, preferably 1.5 to 2.5 wt %, and more preferably 2.0 to 2.5 wt % with respect to the entire cast iron material. When the Si content is too small, there is a tendency that curing of the base material is not accelerated and the base material itself becomes fine to remarkably decline machinability, while when the content is too large, it is liable that extrication of carbon proceeds excessively and the toughness declines.

Mn (manganese) is compounded with S (sulfur) to form manganese sulfide and has an effect of suppressing an adverse effect caused by mixing of S into cast iron, an effect of making the structure fine, an effect of graphitization caused by adding Ni to improve the matrix. A content of Mn is preferably 0 to 0.8 wt % (note that 0 is not included) with respect to the entire cast iron. When the Mn content is too large, there is a tendency that the structure is made noticeably fine, cast iron becomes brittle and the machinability declines.

Since Ni (nickel) does not form carbide in cast iron, there are effects of accelerating graphitization, suppressing arising of white pig iron, and homogenizing the structure and hardness. A content of Ni is 3.5 to 5.5 wt %, preferably 4.0 to 5.0 wt %, and more preferably 4.2 to 4.5 wt % with respect to the entire cast iron material. Particularly, by setting the Ni content to be within the above ranges, the matrix can become martensitic. When the Ni content becomes too small, it is liable that the above effects cannot be obtained, while when the content is too large, it is liable that residual austenite in the matrix becomes bainitic and strength of the cast iron declines.

Cr (chrome) forms fine carbide having high hardness and has an effect of improving wear resistance and matrix strength. A content of Cr is 2.0 to 6.5 wt %, preferably 0.2.5 to 6.0 wt %, and more preferably 2.6 to 5.5 wt % with respect to the entire cast iron material. When the Cr content is set to be 2.0 wt % or more, preferably 2.5 wt % or more, and more preferably 2.6 wt % or more, it becomes possible to bring carbide of Cr into a solid-solution on cementite. Particularly, when the cementite having the solid solution of carbide of Cr is combined with martensitic matrix, an effect of improving hardness of cast iron can be obtained. When the Cr content is too small, it is liable that the above effect cannot be obtained, while when the content is too large, it is liable that hardness when the base material is separated from the mold becomes too high, machinability is deteriorated, and cutting becomes difficult.

In the present invention, particularly by setting the Ni content to be in the above ranges, matrix of the cast iron material can become martensitic. As a result that the matrix becomes martensitic, the cast iron material can be made highly strong. On the other hand, Ni also has an effect of accelerating graphitization. Therefore, when the Ni content is too large, an amount of graphitized carbon becomes too large, and strength of the cast iron material tends to decline.

Thus, in the present invention, by furthermore adding a predetermined amount of Cr as above, Cr and carbon are compounded to form carbide of Cr. Therefore, since carbon can be made to be carbide of Cr by adding Cr, an increase of a graphite amount (graphitization of carbon) caused by adding Ni can be suppressed. At the same time, by adding a predetermined amount of Cr as above, fine and highly hard carbide is formed, so that wear resistance can be improved. Particularly, as a result that the carbide of Cr is brought into a solid-solution on cementite, and the cementite with the solid solution of Cr is combined with the martensitic matrix, hardness of the cast iron can be improved.

Furthermore, while it will be explained in detail later on, by setting a component composition of the cast iron to be within a predetermined range as above, and forcibly and preferentially cooling the sliding surfaces 5 and 10 at a higher cooling rate than that on other parts at the time of cooling and curing a molten metal in the production process, the cast iron structure on the sliding surfaces can be made fine, and hardness and wear resistance of the sliding surfaces can be particularly improved.

As the above inevitable impurities, for example, P (phosphor) and S (sulfur), etc. are mentioned, and the smaller a content of the inevitable impurities is, the more preferable.

P is compounded with iron to form steadite (Fe₃P) and has a tendency of decreasing cutting property of the cast iron and making the cast iron brittle. Accordingly, the smaller a content of P is, the more preferable; and the content is 0.5 wt % or less, more preferably 0.3 wt % or less with respect to the entire cast iron material.

S has a tendency to heighten a coagulation point of the cast iron, deteriorate a flow property of a molten metal and make the cast iron brittle. Therefore, the smaller a content of 8 is, the more preferable; and the content is 0.5 wt % or less, more preferably 0.1 wt % or less, furthermore preferably 0.05 wt % or lose, and particularly preferably 0.02 wt % or less with respect to the entire cast iron material.

In the present embodiment, the cast iron material of the present invention is used as a material of forming the floating seal rings 2 and 7 on the stationary side and rotatable side, so that it is possible to heighten the hardness. The hardness of the floating seal rings can be preferably 62 or more, more preferably 64 or more, and furthermore preferably 65 or more in the Rockwell hardness HRC.

Production Method of Floating Seal Rings 2 and 7 on Stationary Side and Rotatable Side

The floating seal rings 2 and 7 on the stationary side and the rotatable side composing the floating seal apparatus 1 of the present embodiment are produced by preparing raw materials to form cast iron, melting the same to molten metal, and cooling and curing the molten metal in a mold.

First, raw materials are prepared, so that a composition of the cast iron after casting becomes the above composition, and the raw materials are melt in a melting furnace, etc. to obtain a molten metal. The raw materials are not particularly limited and coke, pig iron and alloy iron, etc. may be mentioned.

Next, the thus obtained molten metal is cast in a mold, then, cooled to be cured in the mold, and a floating seal ring formed by a cast iron material is obtained. In the present embodiment, at the time of cooling and curing the molten metal in the mold, it is preferable to use a mold configured that sliding surfaces 5 and 10 to be seal surfaces are forcibly and preferentially cooled at a higher cooling rate comparing with that on other parts, and a position of the sliding surfaces is preferentially cooled comparing with other parts. As a method of forcibly and preferentially cooling the sliding surface position in the mold, for example, a method of flowing a coolant to near the sliding surface position for cooling, a mold casting method, and centrifugal casting method, etc. may be mentioned.

By using a mold as above and forcibly and preferentially cooling the sliding surfaces 5 and 10 at a higher cooling rate comparing with that on other parts, a fine structure can be formed on the sliding surface of the floating seal ring. As such a fine structure, a structure wherein dendritic cementite and fine carbides mainly containing Cr are dispersed and the matrix structure is selected from perlite, bainite and martensite or a mixed structure of these, is preferable.

The cooling rate at the time of cooling and curing as above is, for example, when the cooling rate (° C./min.) at the sliding surface position of the above seal material is C_(R)1 and the cooling rates (° C./min.) on other parts is C_(R)2, preferably 1≦C_(R)1/C_(R)2≦2.5, more preferably 1≦C_(R)1/C_(R)2≦2.00, and furthermore preferably 1<C_(R)1/C_(R)2≦2.0,.

Alternately, the cooling rate of the sliding surfaces 5 and 10 is preferably 300 to 700° C./min., and more preferably 500 to 700° C./min. When the cooling rate is too slow or too fast, it is liable that the fine structure explained above is hard to be formed, so that the cooling rate is preferably within the above ranges.

Note that, in the present embodiment, it is significant that the fine structure explained above is formed on the sliding surfaces S and 10 under the above cooling condition, therefore, it is sufficient if the cooling under the above condition is performed at 400 to 500° C. or so, which is a temperature that the fine structure is formed. Namely, the cooling condition after forming the fine structure on the sliding surfaces 5 and 10 is not particularly limited and may be suitably selected.

In the present embodiment, by forming the fine structure, wherein dendritic cementite and fine carbides mainly containing Cr are dispersed, on the sliding surface under the above cooling condition, strength and hardness of the cast iron can be improved. Particularly, as a result that fine cementite and fine carbides mainly containing Cr are formed, abrasion wear caused by a loss of coarse cementite and brittle structure, for example as exhibited in white pig iron, can be effectively prevented.

Also, when the matrix structure of the above fine structure is made to be preferably a mixed structure of perlite, bainite and martensite, more preferably a mixed structure chiefly consisting martensite, and furthermore preferably a mixed structure of perlite and martensite, wherein martensite is the main body, matrix hardness can be improved.

Note that, in the present embodiment, formation of the above fine structure on the sliding surface can be attained by making a component composition of the cast iron to be the composition of the present invention. Particularly, by controlling an adding amount of Ni and Cr, depth of chill on the chill structure forming the fine structure can be stabilized.

The floating seal apparatus 1 comprising the floating seal rings 2 and 7 on the stationary side and the rotatable side of the present invention produced by the above explained process has high hardness and excellent wear resistance and can be suitably used as a seal for track rollers of construction machines and vehicles.

Note that the present invention is not limited to the above embodiments and variously modified within the scope of the present invention.

For example, in the above embodiments, a floating seal was taken as an example of a seal material according to the present invention, but the seal material according to the present invention is not limited to the floating seal and may be any seal material as far as it is formed by cast iron material having the above composition.

EXAMPLE

Below, the present invention will be explained based on furthermore detailed examples, but the present invention is not limited to these examples.

First, raw materials were prepared so that respective component compositions shown in Table 1 are obtained, thermal treatment (heating melting) at 1600° C. was performed on the raw materials, and the result was cooled at a cooling rate of 500° C./min. to obtain samples 1 to 5 of a cast iron material. Also, chrome-molybdenum cast metal was prepared as a sample 6, and three kinds of Ni-hard cast metals were prepared as samples 7 to 9.

Next, measurement of Rockwell hardness, a wear resistance test and corrosion resistance test were made on the respective cast iron material samples.

Measurement of Rockwell hardness was made on sliding surfaces of cast iron material samples 1 to 9 by making a shape of the samples a seal size shape having an outer diameter ø of 90.1 mm and using a Rockwell hardness testing machine. The measurement results are shown in Table 1.

The wear resistance test was conducted by preparing a stationary test piece in a seal size shape having an outer diameter ø of 90.1 mm and a rotatable test piece in the same shape by using the samples 1 and 6 and producing a floating seal apparatus as shown in FIG. 1. Here, the stationary test piece corresponds to the floating seal ring 2 on the stationary side, and the rotatable test piece corresponds to the floating seal ring 7 on the rotatable side. The test atmosphere was a mixture of 84 wt % of mud (Arizona test Dust) and 14 wt % of water on the outer circumferential side of the stationary test piece and rotatable test piece and lubricating oil on the inner circumferential side. The test condition was to rotate the rotatable test piece at 200 rpm under a condition of “rotating in the forward direction for 20 seconds, posing for 20 seconds, rotating in the backward direction for 20 seconds, and posing for 20 seconds”, which was assumed to be one cycle, and the total was 10000 cycles. A worn state of sliding surfaces of the samples 1 and 6 after the wear resistance test is shown in FIG. 2, and a moving amount on the inner circumferential side of the seal band after the wear resistance test is shown in FIG. 3.

The corrosion test was conducted on the samples 1, 6 and 9 by using a test piece in a seal size shape having an outer diameter ø of 90.1 mm and using a salt spray testing device. The test condition was to wash the seal surface with acetone first, then, the testing atmosphere was a saltwater concentration of 5 wt %, a pH of 6.5 to 7.2, a temperature of 35° C. and humidity of 95 to 98%, and the testing time was one hour. After spraying saltwater, the test piece was washed with an alkali solution, furthermore, washed away with nonionic water to remove excessive corrosive, then, corrosion percentage on the seal surface was evaluated.

Table 1 TABLE 1 Sam- Cast Iron Material ple Component Composition (wt %) No. C Si Mn Cr Ni Mo V P S Structure HRC 1 Example 3.64 2.20 0.44 5.18 4.68 0.00 0.00 0.08 0.01 Martensitic 67 Matrix Fine Structure on Perlite Matrix 2 Example 3.68 2.04 0.35 4.02 4.43 0.00 0.00 0.28 0.01 Martensitic 65 Matrix Fine Structure on Perlite Matrix 3 Example 3.61 2.50 0.35 4.95 4.49 0.00 0.00 0.29 0.01 Martensitic 66 Matrix Fine Structure on Perlite Matrix 3-1 Example 3.40 2.00 0.30˜0.80 3.00 4.50 0.00 0.00 0.30 0.01 Martensitic 63 Matrix Chill Structure on Perlite Matrix 4 Comparative 3.30 2.15 0.79 1.02 0.00 2.30 1.40 0.00 0.01 Martensitic 64 Example Matrix Chill Structure on Perlite Matrix 5 Comparative 3.10 2.25 0.79 0.54 0.00 0.00 0.00 0.00 0.00 Martensitic 47 Example Matrix Chill Structure on Perlite Matrix 6 Comparative 2.90˜3.80 0.70˜1.40 0.30˜0.80 15.0˜18.0 1.00 or 2.00˜4.00 2.00 or 0.00 0.00 Martensitic 60 Example less less Matrix Chill Structure on Perlite Matrix 7 Comparative 3.00˜3.60 0.40˜1.00 0.30˜0.90 1.20˜1.70 3.50˜4.30 0.40 or 0.30˜0.90 0.30 or 0.10 or Martensitic 57˜ Example less less less Matrix Chill 64 Structure on Perlite Matrix 8 Comparative 3.15˜3.35 1.00˜1.20 0.30˜0.80 1.40˜2.50 3.30˜3.80 0.00 0.00 0.30 or 0.15 or Martensitic 56 Example less less Matrix Chill Structure on Perlite Matrix 9 Comparative 2.90˜3.80 2.00˜2.50 0.80 or 0.20 or 4.00˜5.00 0.00 0.00 0.10˜0.50 0.15 or Martensitic 60 Example less less less Matrix Chill Structure on Perlite Matrix Note that the rest of the component composition is Fe.

Evaluation 1

Table 1 shows a component composition, cast iron metal structure and Rockwell hardness of each of the samples 1 to 9. Note that the cast iron metal structure was determined by observing the surface of the cast iron material by using a metal microscope.

From Table 1, the example samples 1 to 3-1 of the present invention had a component composition forming the cast iron material of within the range of the present invention, and the surface structure of the cast iron material was formed by martensitic matrix fine structure on perlite matrix, so that the surface hardness resulted in being high as 67, 65, 66 and 65 in HRC, respectively. On the other hand, in the samples 4 to 9 as comparative examples, wherein the component composition was out of the range of the present invention, the surface structure of the cast iron material became a martensitic matrix chill structure on perlite matrix, and the surface hardness became low as 47 to 64 in HRC, respectively.

From the result, it was confirmed that, by setting the component composition forming the cast iron to be in the range of the present invention and preferably forming a fine structure, a cast iron material having high hardness and excellent wear resistance could be obtained.

Evaluation 2

FIG. 2A and FIG. 2B are views of surface roughness of a worn state on the sliding surface of the samples 1 and 6 after the wear resistance test, wherein FIG. 2A is a view of surface roughness of the sample 1 and FIG. 2B is a view of surface roughness of the sample 6. As is obvious from the drawings, although both of the samples 1 and 6 were much worn on the outer circumferential side for directly contacting water containing mud, it was confirmed that a worn amount was smaller and the wear resistance was superior in the sample 1 when comparing the sample 1 with the sample 6. Accordingly, it was confirmed that by setting the component composition forming the cast iron to be in the range of the present invention and, preferably, making the cast iron structure to be a fine structure, it is possible to obtain a cast iron material having high hardness and excellent wear resistance.

Also, FIG. 3A and FIG. 3B are views of a moving amount on the inner circumferential side of the seal band of the sample 1 and sample 6 after the wear resistance test, wherein FIG. 3A is a view of a moving amount on the inner circumferential side of the sample 1 and FIG. 3B is a view of a moving amount on the inner circumferential side of the sample 6. From the drawings, it can be confirmed that the sample 1 had a smaller moving amount on the inner circumferential side of the seal band when comparing the sample 1 with the sample 6 both on the stationary side and the rotatable side. Note that the moving amount on the inner circumferential side of the sample 1 was 0.28 mm on the stationary side and 0.86 mm on the rotatable side, and that of the sample 6 was 0.44 mm on the stationary side and 1.28 mm on the rotatable side. Accordingly, it was confirmed that by setting the component composition forming the cast iron to be in the range of the present invention, it is possible to make the moving amount on the inner circumferential side of the seal band smaller, so that the cast iron material of the present invention was suitable as a cast iron material for a floating seal ring.

Evaluation 3

As a result of conducting the corrosion test, the example sample 1 had a corrosion percentage of 7%, and the comparative example samples 6 and 9 had corrosion percentages of 9% and 13%, respectively. Therefore, the example sample 1 was confirmed to have superior corrosion resistance to that of the sample 6 as chrome-molybdenum cast iron including a relatively large amount of Cr. Accordingly, it was confirmed from the result that, by making the component composition composing the cast iron to be in the range of the present invention, it is possible to obtain a cast iron material having superior corrosion resistance comparing with the related art. 

1. A cast iron material composed of C, Si, Mn, Ni, Cr and the rest composed of Fe and inevitable impurities, wherein contents of said C, Si, Mn, Ni and Cr with respect to the entire cast iron material are C: 2.9 to 3.8 wt %, Si: 1.0 to 2.5 wt %, Mn: 0 to 0.8 wt % (note that 0 is not included), Ni: 3.5 to 5.0 wt %, and Cr: 2.6 to 5.5 wt %.
 2. The cast iron material as set forth in claim 1, wherein contents of P and S in said inevitable impurities with respect to the entire cast iron material are P: 0.5 wt % or less and S: 0.5 wt % or less.
 3. The cast iron material as set forth in claim 1, wherein a matrix structure is a structure selected from perlite, bainite and martensite, or a mixed structure of these, and has a fine structure consisting of dendritic cementite and carbides of Cr.
 4. The cast iron material as set forth in claim 3, wherein said matrix structure is a mixed structure wherein martensite is the main body.
 5. The cast iron material as set forth in claim 4, wherein said matrix structure is a mixed structure of perlite and martensite, wherein martensite is the main body.
 6. The cast iron material as set forth in claim 1, wherein hardness of said cast iron material is 62 or higher in HRC.
 7. A seal material formed by the cast iron material as set froth in claim
 1. 8. The seal material as set forth in claim 7, wherein a sliding surface of said seal material is formed a structure, wherein the matrix structure is selected from perlite, bainite and martensite or a mixed structure of these, and a fine structure consisting of dendritic cementite and carbides of Cr is included.
 9. A floating sealing ring formed by the seal material as set froth in claim
 7. 10. The floating seal ring as set forth in claim 9, wherein on a sliding surface of said floating seal ring is formed a structure, wherein the matrix structure is selected from perlite, bainite and martensite or a mixed structure of these, and a fine structure consisting of dendritic cementite and carbides of Cr is included.
 11. A production method of a seal material, including steps of casting in a mold a molten metal composed of C, Si, Mn, Ni, Cr and the rest composed of Fe and inevitable impurities, and curing by cooling, wherein contents of said C, Si, Mn, Ni and Cr with respect to the entire molten metal are C: 2.9 to 3.8 wt %, Si: 1.0 to 2.5 wt %, Mn: 0 to 0.8 wt % (note that 0 is not included), Ni: 3.5 to 5.0 wt %, and Cr: 2.6 to 5.5 wt %; wherein a cooling rate at a position of a sliding surface of said seal material is higher than that on other parts when curing by cooling. 